Conventional apparatus and method for measuring curvature of the cornea employing Keratometer or Ophthalmometer are disclosed in a published Bausch and Lomb Keratometer Instruction Manual. The basic principal is optical measurement of corneal curvature of the eye along two principal meridians through use of a Keratometer which consists essentially of a target which is imaged by the cornea, and a telescope to observe this image. Measurement of the target image reveals the corneal curvature in diopters with the variations in curvature, (astigmatism). Operator focusing of the instrument will clarify images of the target mire of the patient's eye. Measuring the horizontal or near horizontal meridians, measuring the vertical or near vertical meridians, and determining the difference between the two measurements indicates the amount of corneal astigmatism. A scale for each of the horizontal and vertical meridians on the instrument indicates the actual diopter power of the cornea in each meridian. With the Keratometer in proper adjustment, a zone approximately 3.0 mm in diameter is measured. When the instrument is properly centered on the cornea the patient looks directly in through the center of the target. There is an aperture in the target center through which the patient sees an image of his own eye. This definite fixation holds the patient's eye centered while observations are made by the operator.
In the case of lens measuring method and apparatus, as distinguished from human cornea, mechanical and electrically conductive means have been employed to measure curvature, for example by measuring the relative positioning of a conductive ring for supporting a lens in either convex or concave orientation while a central movable probe is raised to a point touching the lens as signaled by establishing an electrical circuit. U.S. Patent 4,212,107 discloses such method and apparatus.
U.S. Pat. No. 4,665,914 discloses an instrument for automating radial keratotomy and other corneal operations which includes one or more probe sensors with extendable tips which, by measuring electrical resistivity, are responsive to contact occurring with the corneal surface. Positioning of the probe sensor(s) over various points of the corneal surface provides data signals which enable the surface topography of the cornea to be mapped by a micro-processor. The probe sensor(s) are used with a ring-like fixture attachable by vacuum to the eye and comprised of a fixed outer ring and a movable inner ring, the fixture providing mounting and/or support for these elements while permitting movement to different meridial locations by rotation of the inner ring. One arch element bridging the diameter of the ring fixture supports the probe sensor(s). In a modification, small motors, controlled by the micro-processor, drive the probe sensor(s) in their respective movement over the corneal surface.